<!DOCTYPE>
<html>
  <head>
    <meta charset="utf-8">
    <title>IFE JavaScript Task 01</title>
    <script defer src="task.js"></script>
  </head>
<body>
  <input onkeyup="value=value.replace(/[^0-9]/g,'')" onpaste="value=value.replace(/[^0-9]/g,'')" oncontextmenu = "value=value.replace(/[^0-9]/g,'')" type="text" id="textNum" placeholder="请输入数字"><br/><br/>
  <div id="btn">
    <button>左侧入</button>
    <button>右侧入</button>
    <button>左侧出</button>
    <button>右侧出</button>
  </div>
  <div id="content" style="padding-top: 50px;"></div>
</body>
</html>